Interpretive Summary: Molecular biology (the study of the biology of DNA) has provided opportunities for unlocking secrets of life. Science has benefited from a development of new biotechnologies (biological methods for studying DNA) that have broadened our understanding of how genes (groups of DNA molecules on chromosomes) interact to produce productions that are important to the consuming public (i.e., cancer treatments). Cucumber is a vegetable that is grown widely in the U.S. and throughout the world. Although the basic biology of this crop species (what we can see visually such as fruit yield and quality) has been studied in depth, scientific advances at the molecular DNA level have not been as great. What is known is that cucumber has relatively little amounts of DNA compared to other crop species that makes DNA analysis of cucumber an attractive scientific endeavor. Yield in U.S. processing cucumbers has reached a plateau in the 1980's, and has remained generally unchanged during the 1990's. It is essential that the science of cucumber genetics be understood at the DNA level in order improve cucumber yield in the future. Thus, a study was designed to use new biotechnologies in cucumber to examination its DNA in order to allow plant geneticists and breeders to be more efficient in developing improved varieties. The experiments allowed for the assessment of cucumber DNA, the information of which will greatly increase the ability for scientists to understand the genetics of this economically important crop species. The genetic information gained as a result of this study will benefit the consuming public directly by allowing scientists to develop better varieties more rapidly.

Technical Abstract:
A set of 171 recombinant inbred lines (RIL) were developed from a narrow cross in cucumber (Cucumis sativus L.; 2n = 2x = 14) using the determinate (de), gynoecious (F), standard-sized leaf line G421 and the indeterminate, monoecious, little leaf (ll) line H-19. A 131-point genetic map was constructed using these RILs and 216 F2 individuals to include 14 SSR, 24 SCAR, 27 AFLP, 62 RAPD, 1 SNP, and 3 economically important morphological [F (gynoecy), de (determinate habit), ll (little leaf)] markers. Seven linkage groups spanned 706 cM with mean marker interval of 5.6 cM. The location of F and de was defined by genetic linkage and quantitative trait loci (QTL) analysis to be associated with SSR loci CSWCT28 and CSWCTT14 at 5.0 cM and 0.8 cM, respectively. RIL-based QTL analysis of number of lateral branches in three environments revealed four location-independent factors that cumulatively explained 42% of the observed phenotypic variation. QTL conditioning lateral branching (mlb1.1), fruit length/diameter ratio (ldr1.2), and sex expression (sex1.2) were associated with de. Sex expression was influenced by three genomic regions corresponding to F and de both on linkage Group 1 and a third locus (sex6.1) on linkage Group 6. QTL conditioning number of fruit per plant (fpl1.2), number of lateral branches (mlb1.4), and fruit length/diameter ratio (ldr1.3) were associated with ll. The potential value of these marker-trait associations (i.e., yield components) for plant improvement is portended by the relatively high LOD scores (2.6 to 13.0) and associated R2 values (1.5 % to 32.4 %) that are affiliated with comparatively few genetic factors (perhaps 3 to 10).